I'm prepping for running a Darkest Hour campaign game. I want to run it in 7e rules so I am gravitating toward a WWC London character creation method. In doing so, I'm noticing a few differences between the method in The Darkest Hour and the one on WWC London beyond just simple 6e vs 7e changes.

For instance, in TDH there are bonuses to some skills based on the character's nationality (p. 25). Those bonuses aren't applied in WWC London's method although there is some reference to nationality choices.

I'd like to understand why there is that difference. Can anyone provide some rationale for that?

Presumably the characters in DH who aren't English are more exceptional than the ones in WWC-L who are mostly ordinary folks. Why can't you just use 6e style chargen for the numbers,multiply by 5 where appropriate and then add the background bits from London for the English characters in DH and something similar but different for the foreign chappies. That's what I'd do if I wanted to bother about the differences.

I think that the sort of characters you need for DH, someone who is at home in a foreign country or who escaped from that country through immense hardship, and is strong-willed enough to go back to almost certain death if caught is very different from someone caught up in strange events in their home town.

If you think that fairness or balance is an issue when playing CoC you may not be playing the game correctly
After all everyone dies when eaten by a ghoul regardless if they have an extra few percentiles in skill points.

I suspect that the DH design brief started out with something like characters should represent the characters seen in shows like Secret Army, Wish Me Luck and various books and films like Carve Her Name with Pride and Odette with a link to the Mythos. Almost every one of the people who dropped or flew into Occupied Europe were far from ordinary and many displayed an extraordinary sense of duty and about one quarter of the ones sent to France never survived.

The design brief for WWC-L almost certainly said the characters should represent ordinary people like many of Lovecraft's protagonists and then add in something to give a background/setting to bring the details of life during WW2 in London to life and then add a dash of Mythos.